Various types of vehicles have been developed for transporting personnel, cargo, weapons and other materials over adverse terrain. The overwhelming majority of adverse terrain vehicles have three or more wheel members mounted on each side and are either fitted with pneumatic tires or with a track circumscribing the wheel members. The use of such an arrangement of wheel members offers support to the vehicle at a number of locations along its length, thereby reducing the effect of terrain irregularities, resulting in a smoother ride and increased vehicle stability.
Due to steering limitations imposed by use of three or more wheel members on each side, such adverse terrain vehicles are usually directed along their path of travel by means of skid-steering, whereby the speed of the wheel members positioned on the inside of a selected turn is reduced below the speed of the wheels positioned on the outside of the selected turn to impose a moment on the vehicle in the direction of the selected turn. The imposed moment directs the vehicle into a turn, causing the wheel members to more laterally across the underlying surfaces in varying degrees, depending upon the radius of the turn and the position of the wheel members along the vehicle frame.
In order to facilitate skid-steering, adverse terrain vehicles are typically equipped with a hydrostatic drive system which allows the wheel members of each side of the vehicle to be driven independently of the wheel members on the opposite side of the vehicle. Hydrostatically driven vehicles commonly include at least one engine, or other prime mover, which drives a hydraulic pump on each side of the vehicle. The pumps, in turn, are connected by hydraulic lines to at least one hydraulic motor mounted on each side of the vehicle. The hydraulic motors are generally connected to the wheel members on their respective sides of the vehicle by a mechanical transmission.
During operation, the hydraulic motors drive the wheel members mounted on their respective sides of the vehicle in response to pressurized hydraulic fluid supplied from their associated hydraulic pump through the interconnecting hydraulic lines. Variation in the speed of the wheel members on each side of the vehicle to adjust the velocity of the vehicle and to turn the vehicle is accomplished by varying the displacement of the pumps associated with the wheel members of each side of the vehicle, thereby increasing or decreasing the flow of hydraulic fluid to the motors as is desired. Alternatively, skid-steering of adverse terrain vehicles has been accomplished by applying a braking force to the wheel members positioned on one side of the vehicle, causing the vehicle to turn toward the side in which the braking force is applied.
The operation of conventional adverse terrain vehicles is complicated by the use of such dual braking and drive systems to control the speed and direction of movement of the vehicle. For example, the controls for operation of such vehicles ordinarily include a pair of levers each positionable in front of or behind a neutral position to control the drive and braking systems of one side of the vehicle. For example, forward displacement of a particular lever will increase the output of the hydrostatic drive system of one side of the vehicle, while displacement of the control lever behind the neutral position imposes a braking force on the associated wheel members. Efficient and coordinated control of the steering, braking and velocity of vehicles incorporating such dual controls is often difficult or impossible in extreme situations, such as over very rough terrain and at high speeds, when the risk of damage to equipment and personnel is greatest. In addition, operation of such controls requires the use of both hands of the operator, requiring a second operator, or co-pilot, to control other vehicle functions. Further, the use of such controls requires substantial training due to the dissimilarity from the familiar controls of an automobile.
In addition to difficulties associated with control of velocity and direction of movement, adverse terrain vehicles incorporating hydrostatic drive systems are incapable of satisfactory operation under extreme load conditions, such as when climbing steep grades. In such situations, the load imposed on the prime mover or engine driving the hydraulic pumps of the vehicle increases to the point that the operator must slow the vehicle to a crawl to transverse the hill without stalling the engine. This increases the time required to climb the grade and also causes difficulty in steering the vehicle due to the increase load caused by skid-steering at lower speeds.
The present invention comprises an adverse terrain vehicle including a system for automatically controlling and coordinating a combination of the steering, braking, power output and suspension functions of a vehicle in response to operator commands. The vehicle includes at least two hydrostatic drive systems, each for driving the wheel members on one side of the vehicle independently of the wheel members on the opposing side of the vehicle. The control system includes steering means for directing the vehicle along a path selected by the operator by adjusting the speed of the hydrostatic drive on either side of the vehicle to effect turning of the vehicle. The control system may also include braking means responsive to the commands of the operator input through the steering means for selectively applying braking forces to the wheel members on each side of the vehicle to slow the vehicle, while simultaneously turning the vehicle as directed by the operator.
One aspect of the invention relates to enhancement of the operation of each hydrostatic drive system, which preferably includes a variable displacement hydraulic motor for driving at least one wheel member on each side of the vehicle. Each hydraulic motor, in turn, is driven by pressurized hydraulic fluid supplied by a variable displacement hydraulic pump. The hydraulic pumps of the hydrostatic drive system are driven by at least one prime mover. The control system includes sensing means for sensing a decrease in the power output of the vehicle below a level selected by the operator. In response thereto, an overload protection means is provided for increasing the displacement of the hydraulic motors and decreasing the displacement of the hydraulic pumps in order to increase power output capacity of the vehicle.
The present invention further includes means for sensing the speed of the hydraulic motors on each side of the vehicle. Motor control means responsive to the motor speed sensing means are provided for varying the displacement of the hydraulic motor on each side of the vehicle as the motor speed exceeds a predetermined value and as the motor speed drops below a lower predetermined value. Specifically, the motor control means may be utilized to increase the displacement of the hydraulic motors as they reach the higher speeds to keep the motors within a safe operating speed and to increase the displacement of the hydraulic motors at slower speeds to facilitate acceleration of the vehicle.
In yet another aspect of the invention, the control system includes means responsive to the steering means for adjusting the displacement of at least one of the hydraulic pumps to effect turning of the vehicle when the vehicle is slowing or coasting. This feature of the invention facilitates steering of the vehicle by maintaining sufficient power output to effect a vehicle turn at virtually any speed, regardless of the power output directed by the vehicle operator.
In still another aspect of the invention, the control system includes wheel member positioning means for varying the vertical positioning of the wheel members of the vehicle in response to direction of a vehicle turn by the steering means to facilitate skid steering.
In another aspect of the invention, a tire inflation control system is provided for varying the pressure within the tires of the vehicle while the vehicle is operating.